Solid-state imaging apparatus and imaging system

ABSTRACT

A solid-state imaging apparatus includes a pixel array in which a plurality of unit cells are arranged to form a plurality of rows and a plurality of columns, wherein each of the plurality of unit cells includes a pixel, and the pixel comprising a photoelectric conversion element and an in-pixel readout circuit which outputs a signal corresponding to charges generated in the photoelectric conversion element, power is supplied to the plurality of unit cells via a power supply line and a ground line, and at least one of the plurality of unit cells includes at least a part of a capacitive element having a first electrode connected to the power supply line and a second electrode connected to the ground line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a solid-state imaging apparatus and an imaging system.

2. Description of the Related Art

Japanese Patent Laid-Open No. 2002-344809 discloses an imaging apparatus having vertical shift registers and horizontal shift registers arranged in an image sensor (pixel array). Japanese Patent Laid-Open No. 2002-344809 also discloses an arrangement in which the unit block (the unit to select and drive one row) of vertical shift registers is arranged in one region together with one pixel circuit.

According to the arrangement disclosed in Japanese Patent Laid-Open No. 2002-344809, for example, in the column where the unit block of vertical shift registers is arranged and its neighboring columns, the pixel circuit is susceptible to variations in the power supply potential and the ground potential caused by the operation of the unit block. When the power supply potential and the ground potential vary, noise may be generated in the signal output from the pixel circuit, resulting in poorer image quality.

In addition, an in-pixel readout circuit included in a pixel with a large incident light amount may greatly change the potential of the column signal line and the like, causing variations in the power supply potential and the ground potential, although this does not apply only to the arrangement disclosed in Japanese Patent Laid-Open No. 2002-344809. This influence may ripple through other pixels and, more particularly, neighboring pixels that share the power supply line and the ground line, leading to degradation in image quality.

SUMMARY OF THE INVENTION

The present invention provides a technique that is advantageous in suppressing image quality degradation caused by variations in the potentials of the power supply line and the ground line.

The first aspect of the present invention provides a solid-state imaging apparatus having a pixel array in which a plurality of unit cells are arranged to form a plurality of rows and a plurality of columns, each of the plurality of unit cells comprising a pixel, and the pixel comprising a photoelectric conversion element and an in-pixel readout circuit which outputs a signal corresponding to charges generated in the photoelectric conversion element, wherein power is supplied to the plurality of unit cells via a power supply line and a ground line, and at least one of the plurality of unit cells includes at least a part of a capacitive element having a first electrode connected to the power supply line and a second electrode connected to the ground line.

The second aspect of the present invention provides an imaging system comprising a solid-state imaging apparatus as defined in the first aspect, and a processor which processes a signal output from the solid-state imaging apparatus.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B explain an example of the schematic arrangement of a solid-state imaging apparatus according to an embodiment of the present invention;

FIG. 2 explains an example of the arrangement of an imaging block according to the embodiment of the present invention;

FIG. 3 explains an example of the arrangement of a pixel according to the embodiment of the present invention;

FIGS. 4A and 4B explain an example of the arrangements of shift registers according to the embodiment of the present invention;

FIG. 5 explains an example of a timing chart according to the embodiment of the present invention;

FIG. 6 illustrates unit cell types;

FIG. 7 illustrates unit cell types;

FIG. 8 illustrates examples of the arrangements of a photoelectric conversion element and a capacitive element;

FIG. 9 illustrates other examples of the arrangements of the photoelectric conversion element and the capacitive element; and

FIG. 10 illustrates a radiation imaging system.

DESCRIPTION OF THE EMBODIMENTS

The schematic arrangement of a solid-state imaging apparatus 100 according to an embodiment of the present invention will be described with reference to FIGS. 1A and 1B. The solid-state imaging apparatus 100 can be formed by, for example, arraying a plurality of imaging blocks 101. In this case, an array of a plurality of imaging blocks 101 can form a sensor panel SP having one imaging region. The plurality of imaging blocks 101 can be arranged on a support substrate 102. When the solid-state imaging apparatus 100 uses a single imaging block 101, the single imaging block 101 forms the sensor panel SP. Each of the plurality of imaging blocks 101 may be provided by, for example, forming a circuit element on a semiconductor substrate or forming a semiconductor layer on, for example, a glass substrate and forming a circuit element on the semiconductor layer. Each of the plurality of imaging blocks 101 has a pixel array in which a plurality of pixels are arrayed so as to form pluralities of rows and columns.

The solid-state imaging apparatus 100 may serve as an apparatus which captures an image of radiation such as X-rays or an apparatus which captures an image of visible light. When the solid-state imaging apparatus 100 serves as an apparatus which captures an image of radiation, a scintillator 103 which converts radiation into visible light can typically be provided on the sensor panel SP. The scintillator 103 converts radiation into visible light, which strikes the sensor panel SP and is photoelectrically converted by each photoelectric conversion element on the sensor panel SP (imaging block 101).

An example of the arrangement of each imaging block 101 will be described next with reference to FIG. 2. When the solid-state imaging apparatus 100 uses a single imaging block 101, the single imaging block 101 can be regarded as a solid-state imaging apparatus. The imaging block 101 has a pixel array GA in which a plurality of pixels 201 are arrayed so as to form pluralities of rows and columns and a plurality of column signal lines 208 a are arranged. Each of the plurality of pixels 201 includes a photoelectric conversion element (for example, a photodiode) 202, and an in-pixel readout circuit 203 which outputs a signal (light signal) corresponding to a charge generated by the photoelectric conversion element 202 to the column signal line 208 a. In the pixel array GA, a plurality of column signal lines 208 b may further be arranged, and the in-pixel readout circuit 203 can be configured to output noise generated by itself to the column signal line 208 b in this case. In-pixel readout circuits 203 of two adjacent pixels 201 aligned in the row direction can be axisymmetrically arranged to have, for example, the boundary line between the two pixels 201 as their symmetry axis.

The imaging block 101 includes vertical scanning circuits 204 and horizontal scanning circuits 205. Although the vertical scanning circuit 204 can be placed, for example, between the photoelectric conversion elements 202 on two adjacent columns, it may be placed outside the photoelectric conversion element 202 on the outermost column in the pixel array GA. The vertical scanning circuit 204 includes, for example, a vertical shift register which performs a shift operation in accordance with a first clock CLK1, and scans a plurality of rows in the pixel array GA in accordance with the shift operation by the vertical shift register. The vertical shift register is formed by connecting a plurality of registers in series, and a pulse received by a register in the first stage is sequentially transferred to registers in subsequent stages in accordance with the first clock CLK1. A row corresponding to a register which holds a pulse is to be selected.

Although the horizontal scanning circuit 205 can be placed, for example, between the photoelectric conversion elements 202 on two adjacent rows, it may be placed outside the photoelectric conversion element 202 on the outermost row in the pixel array GA. The horizontal scanning circuit 205 includes, for example, a horizontal shift register which performs a shift operation in accordance with a second clock CLK2, and scans a plurality of columns in the pixel array GA in accordance with the shift operation by the horizontal shift register. The horizontal shift register is formed by connecting a plurality of registers in series, and a pulse received by a register in the first stage is sequentially transferred to registers in subsequent stages in accordance with the second clock CLK2. A column corresponding to a register which holds a pulse is to be selected.

The vertical scanning circuit 204 can be formed by vertically arraying a plurality of unit vertical scanning circuits VSR each including one register that constitutes the vertical shift register. Each unit vertical scanning circuit VSR can be placed in the region sandwiched by a photoelectric conversion element 202 of a pixel belonging to a given column (the leftmost column (that is, the first column) in FIG. 2) and a photoelectric conversion element 202 of a pixel belonging to a column adjacent to the given column (the second column from the left (that is, the second column) in FIG. 2). When a pulse is transferred via the vertical shift register, each unit vertical scanning circuit VSR drives a row select signal VST to active level so that pixels 201 on a row to which it belongs are selected. A light signal and noise from the pixel 201 on the selected row are output to the column signal lines 208 a and 208 b, respectively. Referring to FIG. 2, the column signal lines 208 a and 208 b are indicated by a single line. Pulse signals (start pulses) PULSE1 and PULSE2 are supplied to the input terminals (not shown) of the vertical scanning circuit 204 and horizontal scanning circuit 205, respectively.

The horizontal scanning circuit 205 can be formed by horizontally arraying a plurality of unit horizontal scanning circuits HSR each including one register that constitutes the horizontal shift register. Each unit horizontal scanning circuit HSR is placed in the region sandwiched by two photoelectric conversion elements 202 in each pair of two adjacent pixels (a pair of pixels on the first and second columns, a pair of pixels on the third and fourth columns, . . . ) belonging to one row (the fourth row from the top (that is, the fourth row) in FIG. 2). However, each unit horizontal scanning circuit HSR is not placed in the region sandwiched by two photoelectric conversion elements 202 in two adjacent pixels aligned in the column direction. This arrangement is advantageous to reduce the gap between the photoelectric conversion elements 202 in the column direction. When a pulse is transferred via the horizontal shift register, each unit horizontal scanning circuit HSR controls a switch 207 so that a column to which it belongs is selected, that is, the column signal lines 208 a and 208 b on this column are connected to horizontal signal lines 209 a and 209 b, respectively. That is, a light signal and noise from the pixel 201 on the selected row are output to the column signal lines 208 a and 208 b, respectively, and signals from the selected column (that is, the selected column signal lines 208 a and 208 b) are output to the horizontal signal lines 209 a and 209 b. This implements X-Y addressing. The horizontal signal lines 209 a and 209 b are connected to the inputs of output amplifiers 210 a and 210 b, respectively, and signals output to the horizontal signal lines 209 a and 209 b are amplified by the output amplifiers 210 a and 210 b, respectively, and output via pads 211 a and 211 b, respectively.

The pixel array GA can be regarded as being obtained by arraying a plurality of unit cells 200 each including the pixel 201 so as to form pluralities of rows and columns. The unit cells 200 can include several types. A certain unit cell 200 includes at least a part of the unit vertical scanning circuit VSR. Although a set of two unit cells 200 includes only one unit vertical scanning circuit VSR in the example shown in FIG. 2, one unit cell 200 may include one unit vertical scanning circuit VSR or a set of three or more unit cells 200 may include one unit vertical scanning circuit VSR. Another unit cell 200 includes at least a part of the unit horizontal scanning circuit HSR. Although one unit cell 200 includes one unit horizontal scanning circuit HSR in the example shown in FIG. 2, a set of a plurality of unit cells 200 may include one unit vertical scanning circuit VSR. Still another unit cell 200 includes both at least a part of the unit vertical scanning circuit VSR and at least a part of the unit horizontal scanning circuit HSR. Still another unit cell 200 includes, for example, a unit cell including at least a part of the output amplifier 210 a, a unit cell including at least a part of the output amplifier 210 b, and a unit cell including the switch 207.

An example of the arrangement of each pixel 201 will be described with reference to FIG. 3. The pixel 201 includes the photoelectric conversion element 202 and in-pixel readout circuit 203, as described earlier. The photoelectric conversion element 202 can typically be a photodiode. The in-pixel readout circuit 203 can include, for example, a first amplifier circuit 310, a clamp circuit 320, a light signal sample-and-hold circuit 340, and a noise sample-and-hold circuit 360, and NMOS transistors 343 and 363 and row select switches 344 and 364 in a second amplifier circuit.

The photoelectric conversion element 202 includes a charge storage unit, which is connected to the gate of a PMOS transistor 303 of the first amplifier circuit 310. The source of the PMOS transistor 303 is connected to a current source 305 via a PMOS transistor 304. A first source follower circuit is formed using the PMOS transistor 303 and current source 305. Forming a source follower circuit using the PMOS transistor 303 is effective in reducing 1/f noise. The PMOS transistor 304 serves as an enable switch which enables the first source follower circuit upon being turned on when an enable signal EN supplied to its gate changes to active level. The first amplifier circuit 310 outputs a signal corresponding to the potential of a charge/voltage conversion unit CVC to an intermediate node n1.

In the example shown in FIG. 3, the charge storage unit of the photoelectric conversion element 202 and the gate of the PMOS transistor 303 form a common node, which functions as the charge/voltage conversion unit CVC which changes a charge stored in the charge storage unit to a voltage. That is, the charge/voltage conversion unit CVC has the voltage V (=Q/C) determined by the charge Q stored in the charge storage unit and the capacitance value C of the charge/voltage conversion unit CVC. The charge/voltage conversion unit CVC is connected to a reset potential V_(res) via a PMOS transistor 302 serving as a reset switch. When a reset signal PRES changes to active level, the PMOS transistor 302 is turned on, so the potential of the charge/voltage conversion unit CVC is reset to the reset potential V_(res).

The clamp circuit 320 uses a clamp capacitance 321 to clamp noise output to the intermediate node n1 by the first amplifier circuit 310 in accordance with the reset potential of the charge/voltage conversion unit CVC. In other words, the clamp circuit 320 is a circuit for canceling that noise from a signal output from the first source follower circuit to the intermediate node n1 in accordance with the charge generated by the photoelectric conversion element 202. The noise output to the intermediate node n1 contains kTC noise produced upon resetting. Clamping is done by changing a clamp signal PCL to active level to turn on a PMOS transistor 323, and thereupon changing the clamp signal PCL to inactive level to turn off the PMOS transistor 323. The output terminal of the clamp capacitance 321 is connected to the gate of a PMOS transistor 322. The source of the PMOS transistor 322 is connected to a current source 325 via a PMOS transistor 324. A second source follower circuit is formed using the PMOS transistor 322 and current source 325. The PMOS transistor 324 serves as an enable switch which enables the second source follower circuit upon being turned on when an enable signal EN0 supplied to its gate changes to active level.

A signal output from the second source follower circuit in accordance with the charge generated by photoelectric conversion by the photoelectric conversion element 202 is written in a capacitance 342 as a light signal via a switch 341 when a light signal sampling signal TS changes to active level. A signal output from the second source follower circuit upon turning on the PMOS transistor 323 immediately after the potential of the charge/voltage conversion unit CVC is reset is noise. This noise is written in a capacitance 362 via a switch 361 when a noise sampling signal TN changes to active level. This noise contains the offset component of the second source follower circuit.

When the unit vertical scanning circuit VSR of the vertical scanning circuit 204 drives the row select signal VST to active level, a signal (light signal) held in the capacitance 342 is output to the column signal line 208 a via the NMOS transistor 343 and row select switch 344 in the second amplifier circuit. At the same time, a signal (noise) held in the capacitance 362 is output to the column signal line 208 b via the NMOS transistor 363 and row select switch 364 in the second amplifier circuit. The NMOS transistor 343 in the second amplifier circuit and a constant current source (not shown) provided on the column signal line 208 a form a source follower circuit. Similarly, the NMOS transistor 363 in the second amplifier circuit and a constant current source (not shown) provided on the column signal line 208 b form a source follower circuit.

The pixel 201 may include an add switch 346 which adds light signals from a plurality of adjacent pixels 201. In an add mode, an add mode signal ADD changes to active level, so the add switch 346 is turned on. Thus, the add switch 346 connects the capacitances 342 of adjacent pixels 201 to each other, thereby averaging the light signals. Similarly, the pixel 201 may include an add switch 366 which adds noise signals from a plurality of adjacent pixels 201. When the add switch 366 is turned on, the add switch 366 connects the capacitances 362 of adjacent pixels 201 to each other, thereby averaging the noise signals.

The pixel 201 may have a function for changing the sensitivity. The pixel 201 can include, for example, a first sensitivity change switch 380, a second sensitivity change switch 382, and a circuit element associated with them. When a first change signal WIDE1 changes to active level, the first sensitivity change switch 380 is turned on, so the capacitance value of a first additional capacitance 381 is added to that of the charge/voltage conversion unit CVC. This lowers the sensitivity of the pixel 201. When a second change signal WIDE2 changes to active level, the second sensitivity change switch 382 is turned on, so the capacitance value of a second additional capacitance 383 is added to that of the charge/voltage conversion unit CVC. This further lowers the sensitivity of the pixel 201.

In this manner, adding a function of lowering the sensitivity of the pixel 201 makes it possible to receive a larger amount of light, thus widening the dynamic range. When the first change signal WIDE1 changes to active level, an enable signal EN_(w) may be changed to active level to enable a PMOS transistor 385 to perform a source follower operation, in addition to enabling the PMOS transistor 303 to perform a source follower operation.

Although the vertical scanning circuit 204 can have various arrangements, it can have an arrangement shown in, for example, FIG. 4A. In the vertical scanning circuit 204 shown in FIG. 4A, each unit vertical scanning circuit VSR includes one D-type flip-flop 401, and the first clock CLK1 is supplied to the clock input of the D-type flip-flop 401. The first pulse signal PULSE1 is supplied to the D input of the D-type flip-flop 401 of the unit vertical scanning circuit VSR in the first stage, and received in response to the first clock CLK1. The D-type flip-flop 401 in the first stage outputs a pulse signal having a duration corresponding to one cycle of the first clock CLK1 from its Q output. The Q output of the D-type flip-flop 401 of each unit vertical scanning circuit VSR is used to select a row to which the unit vertical scanning circuit VSR belongs, and is output as a row select signal VST via, for example, a buffer 402. The Q output of the D-type flip-flop 401 of each unit vertical scanning circuit VSR is connected to the D input of the D-type flip-flop 401 of the unit vertical scanning circuit VSR in the next stage.

Although the horizontal scanning circuit 205 can have various arrangements, it can have an arrangement shown in, for example, FIG. 4B. In the horizontal scanning circuit 205 shown in FIG. 4B, each unit horizontal scanning circuit HSR includes one D-type flip-flop 411, and the second clock CLK2 is supplied to the clock input of the D-type flip-flop 411. The second pulse signal PULSE2 is supplied to the D input of the D-type flip-flop 411 of the unit horizontal scanning circuit HSR in the first stage, and received in response to the second clock CLK2. The unit horizontal scanning circuit HSR in the first stage outputs a pulse signal having a duration corresponding to one cycle of the second clock CLK2 from its Q output. The Q output of each unit horizontal scanning circuit HSR is used to select a column to which the unit horizontal scanning circuit HSR belongs, and is output as a column select signal HST via, for example, a buffer 412. The Q output of each unit horizontal scanning circuit HSR is connected to the D input of the D-type flip-flop 411 of the unit horizontal scanning circuit HSR in the next stage. Note that the vertical scanning period that is the scanning period of the vertical scanning circuit 204 is obtained by multiplying the horizontal scanning period of the horizontal scanning circuit 205 by the number of rows in the pixel array GA. The horizontal scanning period is the period of time required to scan all columns in the pixel array GA. Hence, the frequency of the second clock CLK2 supplied to the horizontal scanning circuit 205 which generates the column select signal HST used to select a column is greatly higher than that of the first clock CLK1 supplied to the vertical scanning circuit 204 which generates the row select signal VST used to select a row.

Main signals supplied to each pixel 201 will be described with reference to FIG. 5. The reset signal PRES, enable signal EN, clamp signal PCL, light signal sampling signal TS, and noise sampling signal TN are low-active signals. Although not shown in FIG. 5, the enable signal EN0 can be a signal similar to the enable signal EN. Also, although not shown in FIG. 5, the enable signal EN_(w) can make a transition in the same way as in the enable signal EN when the first change signal WIDE1 becomes active.

First, the enable signal EN becomes active on all rows in the pixel array GA, and the light signal sampling signal TS changes to active level in a pulsed pattern, so a light signal is written in the capacitance 342. Next, the reset signal PRES changes to active level in a pulsed pattern, so the potential of the charge/voltage conversion unit CVC is reset. The clamp signal PCL changes to active level in a pulsed pattern. When the clamp signal PCL is at active level, the noise sampling signal TN changes to active level in a pulsed pattern, so noise is written in the capacitance 362.

A unit vertical scanning circuit VSR corresponding to the first row of the vertical scanning circuit 204 changes its row select signal VST (VST0) to active level. This means that the vertical scanning circuit 204 selects the first row of the pixel array GA. In this state, unit horizontal scanning circuits HSR corresponding to the first to last columns of the horizontal scanning circuit 205 change their column select signals HST (HST0-HSTn) to active level. This means that the horizontal scanning circuit 205 sequentially selects the first to last columns of the pixel array GA. Thus, light signals and noise signals of pixels on the first to last columns on the first row of the pixel array GA are output from the output amplifiers 210 a and 210 b, respectively. After that, a unit vertical scanning circuit VSR corresponding to the second row of the vertical scanning circuit 204 changes its row select signal VST (VST1) to active level. Unit horizontal scanning circuits HSR corresponding to the first to last columns of the horizontal scanning circuit 205 change their column select signals HST (HST0-HSTn) to active level. By performing such an operation for the first to last rows, one image is output from the pixel array GA.

When the unit cell 200 to which the power is supplied via the power supply line and the ground line includes a circuit other than the pixel 201, the operation of the circuit may cause variations in the power supply potential and the ground potential. Then, noise may be generated in the signals output from the unit cell 200 to which the power is supplied via the power supply line and the ground line and other unit cells 200 (especially neighboring unit cells 200) that share the power supply line and the ground line with the unit cell 200 of interest. In addition, the in-pixel readout circuit 203 that is included in the pixel 201 with a large incident light amount may greatly change the potential of the column signal line 208 or the potentials of the signal lines in the in-pixel readout circuit 203. This may cause variations in the power supply potential and the ground potential. In this case as well, noise may be generated in the signals output from the pixel 201 that has caused the variations in the power supply potential and the ground potential and other pixels 201 (especially neighboring pixels 201) that share the power supply line and the ground line with the pixel 201 of interest. In this embodiment, the pixel array GA and, more specifically, all or some of the plurality of unit cells 200 included in the pixel array GA include at least a part of the capacitive element between the power supply line VDD and the ground line GND. The unit cell 200 may include the capacitive element wholly or partially. In the latter case, a set of a plurality of unit cells 200 can typically include one capacitive element. The capacitive element has a first electrode and a second electrode. The first electrode is connected to the power supply line VDD, and the second electrode is connected to the ground line GND. This enables to suppress image quality degradation caused by variations in the power supply potential and the ground potential.

As described above, the plurality of unit cells 200 included in the pixel array GA can include several types with the pixels 201 in different structures. As illustrated in FIG. 6, the plurality of unit cells 200 included in the pixel array GA can include a unit cell 200 a of first type, a unit cell 200 b of second type, a unit cell 200 c of third type, a unit cell 200 d of fourth type, and a unit cell 200 e of fifth type.

In the example shown in FIG. 6, the unit cell 200 a of first type includes neither circuit element other than the pixel 201 and, more particularly, neither active element such as a MOS transistor nor capacitive element CAP. The unit cell 200 b of second type includes at least a part of the unit vertical scanning circuit VSR and at least a part of the capacitive element CAP in addition to the pixel 201. The unit cell 200 c of third type includes at least a part of the unit horizontal scanning circuit HSR and at least a part of the capacitive element CAP in addition to the pixel 201. The unit cell 200 d of fourth type includes at least a part of the unit vertical scanning circuit VSR, at least a part of the unit horizontal scanning circuit HSR, and at least a part of the capacitive element CAP in addition to the pixel 201. The unit cell 200 e of fifth type includes at least a part of an output amplifier 210 and at least a part of the capacitive element CAP in addition to the pixel 201. In the example shown in FIG. 3, the horizontal scanning circuit 205 scans the plurality of column signal lines (pair of column signal lines) 208 a and 208 b so as to sequentially connect them to the horizontal signal lines 209 a and 209 b.

In the example shown in FIG. 6, the capacitive element CAP is arranged in each of the unit cells 200 b to 200 e including active elements that readily cause variations in the potentials of the power supply line VDD and the ground line GND. In the example shown in FIG. 6, the capacitive element CAP is not arranged in the unit cell 200 a having no active element such as a MOS transistor. However, the capacitive element CAP may be arranged in the unit cell 200 a as well.

Another example of the capacitive element arrangement rule will be described with reference to FIG. 7. In the example shown in FIG. 7, the unit cell 200 a of first type includes no circuit element other than the pixel 201 and, more particularly, no active element such as a MOS transistor but includes at least a part of the capacitive element CAP. The unit cell 200 b of second type includes at least a part of the unit vertical scanning circuit VSR in addition to the pixel 201 but no capacitive element CAP. The unit cell 200 c of the third type includes at least a part of the unit horizontal scanning circuit HSR in addition to the pixel 201 but no capacitive element CAP. The unit cell 200 d of fourth type includes at least a part of the unit vertical scanning circuit VSR and at least a part of the unit horizontal scanning circuit HSR in addition to the pixel 201 but no capacitive element CAP. The unit cell 200 e of fifth type includes at least a part of the output amplifier 210 in addition to the pixel 201 but no capacitive element CAP. In the example shown in FIG. 7, no capacitive element CAP is arranged in each of the unit cells 200 b to 200 e each including part of at least one of the unit vertical scanning circuit VSR, the unit horizontal scanning circuit HSR, and the output amplifier 210. At least a part of the capacitive element CAP is arranged in the unit cell 200 a having none of the unit vertical scanning circuit VSR, the unit horizontal scanning circuit HSR, and the output amplifier 210. This capacitive element arrangement rule is effective when there is no sufficient space to arrange the capacitive element. Note that FIG. 7 illustrates no unit cell including at least a part of at least one of the unit vertical scanning circuit VSR and the unit horizontal scanning circuit HSR in addition to the output amplifier 210. However, providing such a unit cell is also possible. According to the example shown in FIG. 7, no capacitive element CAP is arranged in such a unit cell.

Examples of the arrangements of the photoelectric conversion element 202 and the capacitive element CAP will be described with reference to FIG. 8. An example of the arrangement of the photoelectric conversion element 202 will be explained first. The imaging block 101 can be formed on a substrate made by, for example, epitaxially growing a semiconductor layer 820 of the first conductivity type (for example, n type) on a semiconductor member (not shown) of the first conductivity type. The elements are insulated from each other by an element isolation portion 830. The photoelectric conversion element 202 of each pixel 201 includes, for example, an impurity region (well) 801 of the second conductivity type (for example, p type) formed in the semiconductor layer 820, and impurity regions 802 and 816 of the first conductivity type arranged in the impurity region 801. The impurity concentration to form the first conductivity type is higher in the impurity region 802 than in the impurity region 816. The impurity region 802 is surrounded by the impurity region 816. An impurity region 803 of the first conductivity type is arranged in the impurity region 802. The impurity concentration to form the first conductivity type is higher in the impurity region 803 than in the impurity region 802. An impurity region 804 of the second conductivity type is arranged on the impurity regions 802 and 816. The impurity regions 802, 816, and 803 of the first conductivity type and the impurity regions 801 and 804 of the second conductivity type form a buried photodiode. The upper peripheral portion of the impurity region 801 of the second conductivity type is surrounded by an impurity region 806 of the second conductivity type. The impurity region 806 includes a contact region 809 of the second conductivity type. An impurity region (well) 811 of the first conductivity type is arranged around the impurity region 806. A predetermined potential is applied to the impurity region 801 serving as one electrode of the photoelectric conversion element 202 via the impurity region 806. Charges generated by photoelectrically converting light incident on the photoelectric conversion element 202 are collected by the impurity region 802 and further collected by the impurity region 803. The impurity region 803 serving as the other electrode of the photoelectric conversion element 202 is connected to the in-pixel readout circuit 203.

The capacitive element CAP will be described next. This description will be made assuming that the first conductivity type is the n type, and the second conductivity type is the p type. However, the first conductivity type may be the p type, and the second conductivity type may be the n type. The capacitive element CAP can be formed using, as a dielectric, an oxide film formed in the gate oxide film forming process. More specifically, the capacitive element CAP can be formed by, for example, the impurity region 816 serving as the first electrode connected to the power supply line VDD, a polysilicon electrode 815 serving as the second electrode connected to the ground line GND, and an oxide film 814 arranged between them. The oxide film 814 can be formed in, for example, the gate oxide film forming process. The polysilicon electrode 815 can be formed in, for example, the gate electrode forming process. The impurity region 816 of the first conductivity type can be formed in an impurity region (well) 812 of the second conductivity type formed on the semiconductor layer 820 of the first conductivity type. The ground line GND can be connected to the impurity region 812 via a contact region 813.

Another example of the arrangement of the capacitive element CAP will be described next with reference to FIG. 9. This description will be made assuming that the first conductivity type is the n type, and the second conductivity type is the p type. However, the first conductivity type may be the p type, and the second conductivity type may be the n type. The capacitive element CAP can be formed by the p-n junction of the semiconductor layer (well) 820 of the first conductivity type and an impurity region 850 of the second conductivity type. The semiconductor layer (well) 820 of the first conductivity type is connected to the power supply line VDD via a contact region 852 of the first conductivity type. The impurity region 850 of the second conductivity type is connected to the ground line GND via a contact region 851 of the second conductivity type. A reverse bias is applied to the p-n junction so that it functions as the capacitive element CAP.

FIG. 10 illustrates an example in which the solid-state imaging apparatus according to the present invention is applied to an X-ray diagnostic system (radiation imaging system). The radiation imaging system includes a radiation imaging apparatus 6040 and an image processor 6070 which processes a signal output from the radiation imaging apparatus 6040. The radiation imaging apparatus 6040 serves as an apparatus to which the solid-state imaging apparatus 100 mentioned above is applied so as to capture radiation as illustrated in FIG. 1B. X-rays 6060 emitted by an X-ray tube (radiation source) 6050 are transmitted through a chest 6062 of a patient or a subject 6061, and enter the radiation imaging apparatus 6040. The incident X-rays bear the information of the interior of the body of the subject 6061. The image processor (processor) 6070 processes a signal (image) output from the radiation imaging apparatus 6040, and can display the image on, for example, a display 6080 in a control room based on the signal obtained by processing.

Also, the image processor 6070 can transfer the signal obtained by processing to a remote site via a transmission path 6090. This makes it possible to display the image on a display 6081 placed in, for example, a doctor room at another site or record the image on a recording medium such as an optical disk. The recording medium may be a film 6110, and a film processor 6100 records the image on the film 6110 in this case.

The solid-state imaging apparatus according to the present invention is also applicable to an imaging system which captures an image of visible light. Such an imaging system can include, for example, the solid-state imaging apparatus 100 and a processor which processes a signal output from the solid-state imaging apparatus 100. The processing by the processor can include at least one of, for example, processing of converting the image format, processing of compressing the image, processing of changing the image size, and processing of changing the image contrast.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2010-155255, filed Jul. 7, 2010, which is hereby incorporated by reference herein in its entirety. 

What is claimed is:
 1. A solid-state imaging apparatus having a pixel array in which a plurality of unit cells are arranged to form a plurality of rows and a plurality of columns, each of the plurality of unit cells comprising a pixel, and the pixel comprising a photoelectric conversion element and an in-pixel readout circuit which outputs a signal corresponding to charges generated in the photoelectric conversion element, wherein power is supplied to the plurality of unit cells via a power supply line and a ground line, and at least one of the plurality of unit cells includes at least a part of a capacitive element having a first electrode connected to the power supply line and a second electrode connected to the ground line.
 2. The apparatus according to claim 1, wherein each of the unit cells which form at least one column of the pixel array includes at least a part of a unit vertical scanning circuit, and a set of the unit vertical scanning circuits forms a vertical scanning circuit configured to scan the plurality of rows, and the plurality of unit cells include a unit cell including at least a part of the unit vertical scanning circuit and at least a part of the capacitive element.
 3. The apparatus according to claim 1, wherein each of the unit cells which form at least one row of the pixel array includes at least a part of a unit horizontal scanning circuit, and a set of the unit horizontal scanning circuits forms a horizontal scanning circuit configured to scan the plurality of columns, and the plurality of unit cells include a unit cell including at least a part of the unit horizontal scanning circuit and at least a part of the capacitive element.
 4. The apparatus according to claim 1, wherein the pixel array comprises a plurality of column signal lines to be driven by the pixels, and a horizontal signal line to be connected to a selected one of the plurality of column signal lines, and the plurality of unit cells include a unit cell including at least a part of an output amplifier which amplifies a signal output to the horizontal signal line and at least a part of the capacitive element.
 5. The apparatus according to claim 1, wherein the pixel array comprises a plurality of column signal lines to be driven by the pixels of the unit cells, each of the unit cells which form one of the plurality of columns of the pixel array includes at least a part of a unit vertical scanning circuit, and a set of the unit vertical scanning circuits forms a vertical scanning circuit configured to scan the plurality of rows, each of the unit cells which form one of the plurality of rows of the pixel array includes at least a part of a unit horizontal scanning circuit, and a set of the unit horizontal scanning circuits forms a horizontal scanning circuit configured to scan the plurality of columns so as to sequentially connect the plurality of column signal lines to a horizontal signal line, and the plurality of unit cells include a unit cell in which the capacitive element is not arranged, and at least a part of at least one of the unit vertical scanning circuit, the unit horizontal scanning circuit, and an output amplifier which amplifies a signal output to the horizontal signal line is arranged, and a unit cell in which none of the unit vertical scanning circuit, the unit horizontal scanning circuit, and the output amplifier is arranged, and at least a part of the capacitive element is arranged.
 6. An imaging system comprising: a solid-state imaging apparatus defined in claim 1; and a processor which processes a signal output from the solid-state imaging apparatus.
 7. The apparatus according to claim 1, wherein one of the first electrode and the second electrode includes an impurity region in a semiconductor substrate, and the other one of the first electrode and the second electrode includes a polysilicon electrode, and wherein the capacitive element further comprises an oxide film arranged between the impurity region and the polysilicon electrode.
 8. The apparatus according to claim 1, wherein the capacitive element comprises: a semiconductor layer of a first conductivity type, and an impurity region of a second conductivity type arranged to form a junction with the semiconductor layer, and wherein one of the first electrode and the second electrode includes a first contact region of the first conductivity type configured to supply bias to the semiconductor layer, and the other one of the first electrode and the second electrode includes a second contact region of the second conductivity type configured to supply bias to the impurity region.
 9. The apparatus according to claim 1, further comprising: a scintillator configured to convert radiation into visible light, wherein the photoelectric conversion element generates the charges based on the visible light from the scintillator.
 10. An X-ray diagnostic system comprising: a solid-state imaging apparatus defined in claim 9; and a processor which processes a signal output from the solid-state imaging apparatus. 